1. Technical Field of the Invention
This invention relates generally to radio communication technology and more particularly to transformers used within the radio communication technology.
2. Description of Related Art
Two-way radios, which may be incorporated in wireless communication devices, are known to include an antenna, a transformer, an antenna switch, a receiver section, and a transmitter section. The antenna switch couples either the receiver section or the transmitter section to the antenna via the transformer. The transformer may be a transformer balun (balanced/unbalanced) and is generally used to convert single ended signals into differential signals and conversely to convert differential signals into single ended signals. For example, received RF signals via the antenna are converted into differential signals, which are provided to a low noise amplifier of the receiver section. Conversely, differential signals from a power amplifier of the transmitter section are converted into single ended signals, which are provided to the antenna.
As the demand for integrated circuit radios increases, many attempts have been made to integrate transformers and/or transformer baluns onto radio frequency integrated circuits. However, such integration has been limited due to flux leakage, capacitive coupling limits, and significant series resistance. To reduce these limitations, advances have been made in transformer IC design including coplanar interleaved transformers, toroidal and concentric transformers, overlay transformers and symmetric coplanar transformers. Coplanar interleaved transformers have the primary and secondary windings interleaved on the same integrated circuit layer, where the primary and secondary windings are constructed of planer metal traces. While coplanar interleaved transformers reduces size and resistance and are widely used, they suffer from how quality (Q) factor, small coupling coefficients, and, if used as a balun, the center tap is often at an undesirable location, resulting in an asymmetric geometry. As is known, asymmetry of a transformer winding causes an imbalance in the resulting differential signal and/or an imbalance in the resulting single ended signal from a differential signal.
Toroidal and concentric transformers have the primary and secondary windings on several dielectric layers of an integrated circuit. Each layer includes one or more primary and secondary turns, where turns on different layers are coupled in series using vias. Each of the primary turns, on each layer, is constructed around the secondary turns on the same layer. While such toroidal and concentric transformers are well suited for multi-layer structures, they suffer from weak coupling, inconvenient center tap locations, and are asymmetrical.
Overlay transformers include a primary spiral inductor on a top layer and a secondary spiral inductor on a lower layer. Such transformers have high coupling coefficients and relatively small area; however, the secondary is asymmetrical creating a loading asymmetry.
Symmetric coplanar transformers include the primary and secondary windings on the same layer with interconnecting bridges on lower layers. While such transformers have high symmetry, they have weak magnetic coupling and are usually large for desirable inductor values.
While each of these various embodiments of on-chip transformers have utility and certain applications they do not provide multiple uses for various applications. Therefore, a need exists for a multi-use on-chip transformer that is small, provides reasonable inductance values, has a high quality factor, reduces resistance and has a high coupling coefficient.
The on-chip multiple tap transformer and inductor of the present invention substantially meets these needs and others. One embodiment of an on-chip multiple tap transformer balun in accordance with the present invention includes a 1st winding and a 2nd winding having two portions. The 1st winding is on a 1st layer of an integrated circuit and is operably coupled for a single ended signal. The 1st and 2nd portions of the 2nd winding are on a 2nd layer of the integrated circuit. The 1st portion of the 2nd winding includes a 1st node, a 2nd node, and a tap. The 1st node is operably coupled to receive a 1st leg of a 1st differential signal and the 2nd node is coupled to a reference potential. The tap of the 1st portion is operably coupled for a 1st leg of a 2nd differential signal. The 2nd portion of the 2nd winding includes a 1st node, a 2nd node, and a tap. The 1st node is operably coupled to receive a 2nd leg of the 1st differential signal and the 2nd node is operably coupled to the reference potential. The tap of the 2nd portion is coupled for a 2nd leg of the 2nd differential signal. The 1st and 2nd portions of the 2nd winding are symmetrical with respect to the 1st and 2nd nodes and with respect to the tap nodes. Such an on-chip multiple tap transformer balun may be used to convert single ended signals into one or more differential signals. Further, the on-chip multiple tap transformer balun may be used to convert one or more differential signals into a single ended signal.
Another embodiment of a multi-tap differential inductor in accordance with the present invention includes a 1st winding and a 2nd winding. The 1st winding is on a 1st layer of an integrated circuit and is coupled for a single ended signal. The 2nd winding is on a 2nd layer of the integrated circuit and is coupled to receive 1st and 2nd differential signals. To receive such differential signals, the 2nd winding includes 1st and 2nd nodes that are coupled to receive the 1st differential signal and 1st and 2nd taps to receive the 2nd differential signal. A 3rd tap of the secondary is coupled to a reference potential. The 2nd winding is symmetrical about the 3rd tap to produce a symmetrical on-chip multi-tap transformer balun.
An embodiment of an on-chip multi-tap differential inductor includes a 1st winding and a 2nd winding. Each winding is on the same layer of an integrated circuit. The 1st winding includes a 1st node that is coupled to receive a 1st leg of a differential signal and a 2nd node coupled to a reference potential. The 1st winding also includes a tap that is operably coupled to receive a 1st leg of a 2nd differential signal. The 2nd winding includes a 1st node coupled to receive a 2nd leg of the 1st differential signal and a 2nd node coupled to the reference potential. The 2nd winding further includes a tap operably coupled for a 2nd leg of the 2nd differential signal. The 2nd winding is substantially symmetrical to the 1st winding and the tap of the 1st winding is substantially symmetrical to the tap of the 2nd winding.
The various embodiments of multiple tap differential transformer baluns and differential inductors provide for multiple uses in various applications including radio frequency integrated circuits. By including one or more sets of taps, an on-chip multi-tap transformer balun or inductor, the transformer or inductor may be used in a variety of different manners, which may correspond to different operating frequencies, different desired inductancies, different transformer ratios, et cetera.